U.S. patent application number 11/026754 was filed with the patent office on 2005-08-18 for fluoropolymer coating compositions with multifunctional fluoroalkyl crosslinkers for anti-reflective polymer films.
Invention is credited to Cao, Chuntao, Fukushi, Tatsuo, Jing, Naiyong, Klun, Thomas P., Qiu, Zai-Ming, Schultz, William J., Tatge, Timothy J., Walker, Christopher B. JR..
Application Number | 20050182199 11/026754 |
Document ID | / |
Family ID | 36218068 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050182199 |
Kind Code |
A1 |
Jing, Naiyong ; et
al. |
August 18, 2005 |
Fluoropolymer coating compositions with multifunctional fluoroalkyl
crosslinkers for anti-reflective polymer films
Abstract
An economic, optically transmissive, stain and ink repellent,
durable low refractive index fluoropolymer composition for use in
an antireflection film or coupled to an optical display. In one
aspect of the invention, the composition is formed from the
reaction product of a fluoropolymer and a fluoroalkyl containing
multi-olefinic crosslinker. In another aspect of the invention, the
composition further includes surface modified inorganic
nanoparticles.
Inventors: |
Jing, Naiyong; (Woodbury,
MN) ; Cao, Chuntao; (Woodbury, MN) ; Fukushi,
Tatsuo; (Woodbury, MN) ; Tatge, Timothy J.;
(Crystal, MN) ; Walker, Christopher B. JR.; (St.
Paul, MN) ; Klun, Thomas P.; (Lakeland, MN) ;
Schultz, William J.; (North Oaks, MN) ; Qiu,
Zai-Ming; (Woodbury, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Family ID: |
36218068 |
Appl. No.: |
11/026754 |
Filed: |
December 30, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11026754 |
Dec 30, 2004 |
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10900692 |
Jul 27, 2004 |
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10900692 |
Jul 27, 2004 |
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09730867 |
Dec 6, 2000 |
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6767295 |
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Current U.S.
Class: |
525/326.3 ;
524/544; 525/326.4 |
Current CPC
Class: |
G02B 1/111 20130101;
Y10T 428/269 20150115; A63B 37/0004 20130101 |
Class at
Publication: |
525/326.3 ;
525/326.4; 524/544 |
International
Class: |
C08F 008/00 |
Claims
What is claimed is:
1. A low refractive index composition for use in an antireflection
coating for an optical display, the composition comprising the
reaction product of: a fluoropolymer; and a fluoroalkyl-containing
multi-olefinic crosslinker.
2. The composition of claim 1, wherein said fluoropolymer is
selected from the group consisting of a TFE copolymer, a HFP
copolymer, THV, and FKM.
3. The composition of claim 2, wherein said fluoropolymer comprises
a fluoroelastomer.
4. The composition of claim 3, said fluoroelastomer is selected
from the group consisting of a Cl-containing fluoroelastomer,
Br-containing fluoroelastomer, an I-containing fluoroelastomer, and
a CN-containing fluoroelastomer.
5. The composition of claim 1, wherein said fluoroalkyl-containing
multi-olefinic crosslinker comprises a perfluoropolyether
multi-acrylate crosslinker.
6. The composition of claim 5, wherein said perfluoropolyether
multi-acrylate crosslinker comprises an HFPO-multiacrylate
crosslinker.
7. The composition of claim 1, wherein said fluoroalkyl-containing
multi-olefinic crosslinker comprises a mono- or multi- (meth)acryl
compound bearing at least one monovalent C1 to C8 fluoroalkyl
moiety.
8. The composition of claim 1, wherein said fluoroalkyl-containing
multi-olefinic crosslinker comprises a mono- or multi- (meth)acryl
compound bearing at least one monovalent C1 to C8 fluoroalkylene
moiety.
9. The composition of claim 1 further comprising a plurality of
surface modified inorganic nanoparticles.
10. The composition of claim 1 further comprising one or more
multi-olefinic compounds bearing at least one monovalent
poly(hexafluoropropylene oxide) (HFPO) moiety.
11. The composition of claim 10 further comprising a compatibilizer
selected from the group consisting of a fluoroalkyl-substituted
monoacrylate, a fluoroalkyl-substituted multiacrylate, a
fluoroalkylene-substituted monoacrylate and a
fluoroalkylene-substituted multi-acrylate.
12. The composition of claim 11, wherein said compatibilizer is
selected from the group consisting of
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.-
sub.2OC(O)CH.dbd.CH.sub.2,
C.sub.4F.sub.9SO.sub.2N(CH.sub.2CH.sub.2OC(O)CH-
.dbd.CH.sub.2).sub.2, and
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub.-
2OC(O)C(CH.sub.3).dbd.CH.sub.2.
13. The composition of claim 11, wherein said compatibilizer
comprises a thiol or a polythiol compatibilizer.
14. The composition of claim 13, wherein said thiol or polythiol
compatibilizer is selected from the group consisting of
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub.2OC(O)CH.sub.2SH,
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub.2OC(O)CH.sub.2CH.sub.2SH,
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub.2SH, and
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH(OC(O)CH.sub.2SH)CH.sub.2OC(O)CH.sub.2-
SH.
15. The composition of claim 10, wherein said mono- or multi-
(meth)acryl compound bearing at least one monovalent
hexafluoropolypropylene oxide moiety has the chemical formula:
R.sub.fpeQ(X).sub.n, wherein R.sub.fpe is a residue of a monovalent
HFPO moiety; wherein Q is a connecting group selected from the
group consisting of an alkylene group, an arylene group, an
arylene-alkylene group, and an alkylene-arylene group; wherein X is
a free-radically reactive group selected from the group consisting
of a meth(acryl) reactive group, an allyl reactive group, and a
vinyl reactive group; and wherein n is 2 to 3.
16. The composition of claim 15, wherein Q is selected from the
group consisting of--(CH.sub.2).sub.m--;
--CH.sub.2O(CH.sub.2).sub.3--; and --C(O)NRCH.sub.2CH.sub.2--,
where R is an H or lower alkyl of 1 to 4 carbon atoms and m is 1 to
6.
17. An antireflection film having a layer of said low refractive
index material of claim 1, said antireflection film further
comprising a high refractive index layer coupled to said layer of
said low refractive index material.
18. An optical device comprising a layer of said low refractive
index material formed according to claim 1.
19. A low refractive index composition for use in an antireflection
coating for an optical display, the composition comprising the
reaction product of: a fluoropolymer; a fluoroalkyl-containing
multi-olefinic crosslinker; and a plurality of surface modified
nanoparticles.
20. A method for forming an optically transmissive, stain and ink
repellent, durable optical display comprising: providing an optical
display having an optical substrate; forming a low refractive index
polymer composition comprising a fluoropolymer and a
fluoroalkyl-containing multi-olefinic crosslinker; applying a layer
of said low refractive index polymer composition to said optical
substrate; and curing said layer to form a cured film.
21. The method of claim 20, wherein providing an optical display
comprises provided an optical display having a hard coat layer
applied to an optical substrate.
22. The method of claim 20, wherein forming a low refractive index
polymer composition comprises reactively coupling a fluoropolymer
and a fluoroalkyl-containing multifunctional olefinic crosslinker.
Description
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
[0001] The present invention relates to antireflective films and
more specifically to low refractive index fluoropolymer coating
compositions for use in antireflection polymer films.
BACKGROUND OF THE INVENTION
[0002] Antireflective polymer films ("AR films") are becoming
increasingly important in the display industry. New applications
are being developed for low reflective films applied to substrates
of articles used in the computer, television, appliance, mobile
phone, aerospace and automotive industries.
[0003] AR films are typically constructed by alternating high and
low refractive index ("RI") polymer layers in order to minimize the
amount of light that is reflected from the optical display surface.
Desirable product features in AR films for use on optical goods are
a low percentage of reflected light (e.g. 1.5% or lower) and
durability to scratches and abrasions. These features are obtained
in AR constructions by maximizing the delta RI between the polymer
layers while maintaining strong adhesion between the polymer
layers.
[0004] It is known that the low refractive index polymer layers
used in AR films can be derived from fluorine containing polymers
("fluoropolymers" or "fluorinated polymers"). Fluoropolymers
provide advantages over conventional hydrocarbon-based materials
relative to high chemical inertness (in terms of acid and base
resistance), dirt and stain resistance (due to low surface energy)
low moisture absorption, and resistance to weather and solar
conditions.
[0005] The refractive index of fluorinated polymer coating layers
can be dependent upon the volume percentage of fluorine contained
within the layer. Increased fluorine content in the layers
typically decreases the refractive index of the coating layer.
However, organic solvent soluble fluoropolymers with low
crystallinity generally have undesired mechanical properties, such
as poor scratching resistance and poor the interfacial adhesion of
the fluoropolymer layer to other polymer or substrate layers to
which the layer is coupled.
[0006] Thus, it is highly desirable to form a low refractive index
layer for an antireflection film having increased fluorine content,
and hence lower refractive index, while improving mechanical
properties by crosslinking and by enhancing interfacial adhesion to
accompanying layers or substrates.
SUMMARY OF THE INVENTION
[0007] The present invention provides an economic and durable low
refractive index fluoropolymer composition for use as a low
refractive index film layer in an antireflective film for an
optical display. The low refractive index composition forms layers
having strong interfacial adhesion to a high index refractive layer
and/or a substrate material.
[0008] In one aspect of the invention, a low refractive index layer
is formed from the reaction product of a fluoropolymer and a
fluoroalkyl containing multi-olefinic crosslinker. The introduction
of the fluoro-component to the multi-olefinic crosslinker enhances
the low surface energy characteristics of the coating, while
maintaining sufficient crosslinking between fluoropolymer and the
multi-olefinic crosslinker. The low surface energy characteristic
is advantageous since it provides a stain-resistant and
easy-to-clean feature to the coating. Moreover, by the nature of
the fluoroalkyl multi-acrylate, the low refractive index properties
of the coating are maintained or even further enhanced. The
fluoroalkyl-component may also help to eliminate the need for a
compatibilizer between the fluoropolymer and the multi-olefinic
crosslinker.
[0009] Further, the mechanical strength and scratch resistance the
low refractive index composition can be enhanced by the addition of
surface functionalized nanoparticles into the fluoropolymer
compositions. Providing functionality to the nanoparticles enhances
the interactions between the fluoropolymers and such functionalized
particles.
[0010] The present invention also provides an article having an
optical display that is formed by introducing the antireflection
film having a layer of the above low refractive index compositions
to an optical substrate. The resultant optical device has an outer
coating layer that is easy to clean, durable, and has low surface
energy.
[0011] Other objects and advantages of the present invention will
become apparent upon considering the following detailed description
and appended claims, and upon reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is perspective view of an article having an optical
display; and
[0013] FIG. 2 is a sectional view of the article of FIG. 1 taken
along line 2-2 illustrating an antireflection film having a low
refractive index layer formed in accordance with a preferred
embodiment of the present invention.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION
[0014] For the following defined terms, these definitions shall be
applied, unless a different definition is given in the claims or
elsewhere in the specification.
[0015] The term "polymer" will be understood to include polymers,
copolymers (e.g. polymers using two or more different monomers),
oligomers and combinations thereof, as well as polymers, oligomers,
or copolymers that can be formed in a miscible blend.
[0016] As used herein, the term "ceramer" is a composition having
inorganic oxide particles, e.g. silica, of nanometer dimensions
dispersed in a binder matrix. The phrase "ceramer composition" is
meant to indicate a ceramer formulation in accordance with the
present invention that has not been at least partially cured with
radiation energy, and thus is a flowing, coatable liquid. The
phrase "ceramer composite" or "coating layer" is meant to indicate
a ceramer formulation in accordance with the present invention that
has been at least partially cured with radiation energy, so that it
is a substantially non-flowing solid. Additionally, the phrase
"free-radically polymerizable" refers to the ability of monomers,
oligomers, polymers or the like to participate in crosslinking
reactions upon exposure to a suitable source of curing energy.
[0017] The term "low refractive index", for the purposes of the
present invention, shall mean a material when applied as a layer to
a substrate forms a coating layer having a refractive index of less
than about 1.5, and more preferably less than about 1.45, and most
preferably less than about 1.42.
[0018] The term "high refractive index", for the purposes of the
present invention, shall mean a material when applied as a layer to
a substrate forms a coating layer having a refractive index of
greater than about 1.5.
[0019] The recitation of numerical ranges by endpoints includes all
numbers subsumed within the range (e.g. the range 1 to 10 includes
1, 1.5, 3.33, and 10).
[0020] As used in this specification and the appended claims, the
singular forms "a", "an", and "the" include plural referents unless
the content clearly dictates otherwise. Thus, for example,
reference to a composition containing "a compound" includes a
mixture of two or more compounds. As used in this specification and
the appended claims, the term "or" is generally employed in its
sense including "and/or" unless the content clearly indicates
otherwise.
[0021] Unless otherwise indicated, all numbers expressing
quantities of ingredients, measurements of properties such as
contact angle and so forth as used in the specification and claims
are to be understood to be modified in all instances by the term
"about." Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the foregoing specification and
attached claims are approximations that can vary depending upon the
desired properties sought to be obtained by those skilled in the
art utilizing the teachings of the present invention. At the very
least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of the claims, each numerical
parameter should at least be construed in light of the number of
reported significant digits and by applying ordinary rounding
techniques. Notwithstanding that the numerical ranges and
parameters setting forth the broad scope of the invention are
approximations, the numerical values set forth in the specific
examples are reported as accurately as possible. Any numerical
value, however, inherently contains certain errors necessarily
resulting from the standard deviations found in their respective
testing measurements.
[0022] The present invention is directed to antireflection
materials used as a portion of optical displays ("displays"). The
displays include various illuminated and non-illuminated displays
panels wherein a combination of low surface energy (e.g.
anti-soiling, stain resistant, oil and/or water repellency) and
durability (e.g. abrasion resistance) is desired while maintaining
optical clarity. The antireflection material functions to decrease
glare and decrease transmission loss while improving durability and
optical clarity.
[0023] Such displays include multi-character and especially
multi-line multi-character displays such as liquid crystal displays
("LCDs"), plasma displays, front and rear projection displays,
cathode ray tubes ("CRTs"), signage, as well as single-character or
binary displays such as light emitting tubes ("LEDs"), signal lamps
and switches. The light transmissive (i.e. exposed surface)
substrate of such display panels may be referred to as a "lens."
The invention is particularly useful for displays having a viewing
surface that is susceptible to damage.
[0024] The coating composition, and reactive product thereof, as
well as the protective articles of the invention, can be employed
in a variety of portable and non-portable information display
articles. These articles include, but are not limited by, PDAs, LCD
TV's (direct lit and edge lit), cell phones (including combination
PDA/cell phones), touch sensitive screens, wrist watches, car
navigation systems, global positioning systems, depth finders,
calculators, electronic books, CD and DVD players, projection
televisions screens, computer monitors, notebook computer displays,
instrument gauges, instrument panel covers, signage such as graphic
displays and the like. These devices can have planar viewing faces,
or non-planar viewing faces such as slightly curved faces. The
above listing of potential applications should not be construed to
unduly limit the invention.
[0025] Referring now to FIG. 1, a perspective view of an article,
here a computer monitor 10, is illustrated according to one
preferred embodiment as having an optical display 12 coupled within
a housing 14. The optical display 12 is a substantially transparent
material having optically enhancing properties through which a user
can view text, graphics or other displayed information.
[0026] As best shown in FIG. 2, the optical display 12 includes an
antireflection film 18 coupled (coated) to an optical substrate 16.
The antireflection film 18 has at least one layer of a high
refraction index layer 22 and a low refractive index layer 20
coupled together such that the low refractive index layer 20 being
positioned to be exposed to the atmosphere while the high
refractive index layer 22 is positioned between the substrate 16
and low refractive index layer 20.
[0027] The optical substrate 16 preferably comprises an inorganic
material, such as glass, or a polymeric organic material such as
polyethylene terephthalate ("PET"), that are well known to those of
ordinary skill in the optical display art. In addition, the
substrate 16 may comprise a hybrid material, having both organic
and inorganic components.
[0028] While not shown, other layers may be incorporated into the
optical device, including, but not limited to, other hard coating
layers, adhesive layers, and the like. Further, the antireflection
material 18 may be applied directly to the substrate 16, or
alternatively applied to a release layer of a transferable
antireflection film and subsequently transferred from the release
layer to the substrate using a heat press or photoradiation
application technique.
[0029] The high refractive index layer 22 is a conventional
carbon-based polymeric composition having a mono and multi-acrylate
crosslinking system.
[0030] The low refractive index coating composition of the present
invention used to form layer 20, in one aspect of the invention, a
low refractive index layer is formed from the reaction product of a
fluoropolymer and a fluoroalkyl containing multi-olefinic
crosslinker. The reaction mechanism for forming the coating
composition is described further below as Reaction Mechanism 1.
[0031] In another preferred approach, inorganic surface
functionalized nanoparticles are added to the low refractive index
composition 20 described in the preceding paragraphs to provide
increased mechanical strength and scratch resistance to the low
index coatings.
[0032] The low refractive index composition that is formed in any
of the preferred approaches is then applied directly or indirectly
to a substrate 16 of a display 12 to form a low refractive index
portion 20 of an antireflection coating 18 on the article 10. With
the invention, the article 10 has outstanding optical properties,
including decreased glare and increased optical transmissivity.
Further, the antireflection coating 18 has outstanding durability,
as well as ink and stain repellency properties.
[0033] The ingredients for forming the various low refractive index
compositions are summarized in the following paragraphs, followed
by the reaction mechanism for forming the coating according to one
preferred approach.
[0034] Fluoropolymer
[0035] Fluoropolymer materials used in the low index coating may be
described by broadly categorizing them into one of two basic
classes. A first class includes those amorphous fluoropolymers
comprising interpolymerized units derived from vinylidene fluoride
(VDF) and hexafluoropropylene (HFP) and optionally
tetrafluoroethylene (TFE) monomers. Examples of such are
commercially available from 3M Company as Dyneon.TM.
Fluoroelastomer FC 2145 and FT 2430. Additional amorphous
fluoropolymers contemplated by this invention are for example
VDF-chlorotrifluoroethylene copolymers, commercially known as
Kel-F.TM. 3700, available from 3M Company. As used herein,
amorphous fluoropolymers are materials that contain essentially no
crystallinity or possess no significant melting point as determined
for example by differential scanning caloriometry (DSC). For the
purpose of this discussion, a copolymer is defined as a polymeric
material resulting from the simultaneous polymerization of two or
more dissimilar monomers and a homopolymer is a polymeric material
resulting from the polymerization of a single monomer.
[0036] The second significant class of fluoropolymers useful in
this invention are those homo and copolymers based on fluorinated
monomers such as TFE or VDF which do contain a crystalline melting
point such as polyvinylidene fluoride (PVDF, available commercially
from 3M Company as Dyneon.TM. PVDF, or more preferable
thermoplastic copolymers of TFE such as those based on the
crystalline microstructure of TFE-HFP-VDF. Examples of such
polymers are those available from 3M under the trade name
Dyneon.TM. Fluoroplastic THV.TM. 200.
[0037] A general description and preparation of these classes of
fluoropolymers can be found in Encyclopedia Chemical Technology,
Fluorocarbon Elastomers, Kirk-Othmer (1993), or in Modern
Fluoropolymers, J. Scheirs Ed, (1997), J Wiley Science, Chapters 2,
13, and 32. (ISBN 0-471-97055-7).
[0038] The preferred fluoropolymers are copolymers formed from the
constituent monomers known as tetrafluoroethylene ("TFE"),
hexafluoropropylene ("HFP"), and vinylidene fluoride ("VDF," "VF2,
"). The monomer structures for these constituents are shown
below:
TFE: CF.sub.2.dbd.CF.sub.2 (1)
VDF: CH.sub.2.dbd.CF.sub.2 (2)
HFP: CF.sub.2.dbd.CF--CF.sub.3 (3)
[0039] The preferred fluoropolymer consists of at least two of the
constituent monomers (HFP and VDF), and more preferably all three
of the constituents monomers in varying molar amounts. Additional
monomers not depicted in (1), (2) or (3) but also useful in the
present invention include perfluorovinyl ether monomers of the
general structure CF.sub.2.dbd.CF--OR.sub.f, wherein R.sub.f can be
a branched or linear perfluoroalkyl radicals of 1-8 carbons and can
itself contain additional heteroatoms such as oxygen. Specific
examples are perfluoromethyl vinyl ether, perfluoropropyl vinyl
ethers, perfluoro(3-methoxy-propyl) vinyl ether. Additional
examples are found in Worm (WO 00/12574), assigned to 3M, and in
Carlson (U.S. Pat. No. 5,214,100).
[0040] For the purposes of the present invention, crystalline
copolymers with all three constituent monomers shall be hereinafter
referred to as THV, while amorphous copolymers consisting of
VDF-HFP and optionally TFE is hereinafter referred to as FKM, or
FKM elastomers as denoted in ASTM D 1418. THV and FKM elastomers
have the general formula (4): 1
[0041] wherein x, y and z are expressed as molar percentages.
[0042] For fluorothermoplastics materials (crystalline) such as
THV, x is greater than zero and the molar amount of y is typically
less than about 15 molar percent. One commercially available form
of THV contemplated for use in the present invention is Dyneon.TM.
Fluorothermoplastic THV.TM. 220, a polymer that is manufactured by
Dyneon LLC, of St. Paul, Minn. Other useful fluorothermoplastics
meeting these criteria and commercially available, for example,
from Dyneon LLC, St. Paul, Minn., are sold under the trade names
THV.TM. 200, THV.TM. 500, and THV.TM. 800. THV.TM. 200 is most
preferred since it is readily soluble in common organic solvents
such as MEK and this facilitates coating and processing, however
this is a choice born out of preferred coating behavior and not a
limitation of the material used a low refractive index coating.
[0043] In addition, other fluoroplastic materials not specifically
falling under the criteria of the previous paragraph are also
contemplated by the present invention. For example, PVDF-containing
fluoroplastic materials having very low molar levels of HFP are
also contemplated by the present invention and are sold under the
trade name Dyneon.TM. PVDF 6010 or 3100, available from Dyneon LLC,
of St. Paul, Minn.; and Kynar.TM. 740, 2800, 9301, available from
Elf Atochem North America Inc. Further, other fluoroplastic
materials are specifically contemplated wherein x is zero and
wherein y is between about 0 and 18 percent. Optionally the
microstructure shown in (4) can also contain additional
non-fluorinated monomers such as ethylene, propylene, or butylene.
Examples of which are commercially available as Dyneon.TM. ETFE and
Dyneon.TM. HTE fluoroplastics.
[0044] For fluoroelastomers compositions (amorphous) useful in the
present invention, x can be zero so long as the molar percentage of
y is sufficiently high (typically greater than about 18 molar
percent) to render the microstructure amorphous. One example of a
commercially available elastomeric compound of this type is
available from Dyneon LLC, St. Paul, Minn., under the trade name
Dyneon.TM. Fluoroelastomer FC 2145.
[0045] Additional fluoroelastomer compositions useful in the
present invention exist where x is greater than zero. Such
materials are often referred to as elastomeric TFE containing
terpolymers. One example of a commercially available elastomeric
compound of this type is available from Dyneon LLC, St. Paul,
Minn., and is sold under the trade name Dyneon.TM. Fluoroelastomer
FT 2430.
[0046] In addition, other fluorelastomeric compositions not
classified under the preceding paragraphs are also useful in the
present invention. For example, propylene-containing
fluoroelastomers are a class useful in this invention. Examples of
propylene-containing fluoroelastomers known as base resistant
elastomers ("BRE") and are commercially available from Dyneon under
the trade name Dyneon.TM. BRE 7200 available from 3M Company of St.
Paul, Minn. Other examples of TFE-propylene copolymer can also be
used are commercially available under the tradename Aflaf.TM.,
available from Asahi Glass Company of Charlotte, N.C.
[0047] In one preferred approach, these polymer compositions
further comprise reactive functionality such as halogen-containing
cure site monomers ("CSM") and/or halogenated endgroups, which are
interpolymerized into the polymer microstructure using numerous
techniques known in the art. These halogen groups provide
reactivity towards the other components of coating mixture and
facilitate the formation of the polymer network. Useful
halogen-containing monomers are well known in the art and typical
examples are found in U.S. Pat. No. 4,214,060 to Apotheker et al.,
European Patent No. EP398241 to Moore, and European Patent No.
EP407937B1 to Vincenzo et al.
[0048] In addition to halogen containing cure site monomers, it is
conceivable to incorporate nitrile-containing cure site monomers in
the fluoropolymer microstructure. Such CSM's are particularly
useful when the polymers are perfluorinated, i.e. contain no VDF or
other hydrogen containing monomers. Specific nitrile-containing
CSM's contemplated by this invention are described in Grootaret et
al. (U.S. Pat. No. 6,720,360, assigned to 3M).
[0049] Optionally halogen cure sites can be introduced into the
polymer microstructure via the judicious use of halogenated chain
transfer agents which produce fluoropolymer chain ends that contain
reactive halogen endgroups. Such chain transfer agents ("CTA") are
well known in the literature and typical examples are:
Br-CF.sub.2CF.sub.2-Br, CF.sub.2Br.sub.2, CF.sub.2I.sub.2,
CH.sub.2I.sub.2. Other typical examples are found in U.S. Pat. No.
4,000,356 to Weisgerber. Whether the halogen is incorporated into
the polymer microstructure by means of a CSM or CTA agent or both
is not particularly relevant as both result in a fluoropolymer
which is more reactive towards UV crosslinking and coreaction with
other components of the network such as the acrylates. An advantage
to use of cure site monomers in forming the co-crosslinked network,
as opposed to a dehydrofluorination approach (discussed below), is
that the optical clarity of the formed polymer layer is not
compromised since the reaction of the acrylate and the
fluoropolymer does not rely on unsaturation in the polymer backbone
in order to react. Thus, a bromo-containing fluoroelastomer such as
Dyneon.TM. E-15472, E-18905, or E-18402 available from Dyneon LLC
of St. Paul, Minn., may be used in conjunction with, or in place
of, THV or FKM as the fluoropolymer.
[0050] In another embodiment the fluoropolymer microstructure is
first dehydrofluorinated by any method that will provide sufficient
carbon-carbon unsaturation of the fluoropolymer to create increased
bond strength between the fluoropolymer and a hydrocarbon substrate
or layer. The dehydrofluorination process is a well-known process
to induced unsaturation and it is used most commonly for the ionic
crosslinking of fluoroelastomers by nucleophiles such as diphenols
and diamines. This reaction is an inherent property of VDF
containing elastomers or THV. A descriptions can be found in The
Chemistry of Fluorocarbon Elastomer, A. L. Logothetis, Prog.
Polymer Science (1989), 14, 251. Furthermore, such a reaction is
also possible with primary and secondary aliphatic monofunctional
amines and will produce a DHF-fluoropolymer with a pendent amine
side group. However, such a DHF reaction is not possible in
polymers which do not contain VDF units since they lack the ability
to lose HF by such reagents.
[0051] In addition to the main types of fluoropolymers useful in
the context of this invention, there is a third special case
involving the use of perfluoropolymers or ethylene containing
fluoropolymers which are exempt form the DHF addition reaction
described above but nonetheless are reactive photochemically with
amines to produce low index fluoropolymer coatings. Examples of
such are copolymers of TFE with HFP or perfluorovinyl ethers, or
2,2-bistrifluoromethyl-4,5-difluoro 1,3 dioxole. Such
perfluoropolymers are commercially available as Dyneon.TM.
Perfluoroelastomer, DuPont Kalrez.TM. or DuPont Teflon.TM. AF.
Examples of ethylene containing fluoropolymers are known as
Dyneon.TM. HTE or Dyneon.TM., ETFE copolymers. Such polymers are
described in the above-mentioned reference of Scheirs Chapters 15,
19 and 22. Although these polymers are not readily soluble in
typical organic solvents, they can be solubilized in such
perfluoroinated solvents such as HFE 7100 and HFE 7200 (available
from 3M Company, St. Paul, Minn.). These types of fluoropolymers
are not easily bonded to other polymers or substrates. However the
work of Jing et al, in U.S. Pat. Nos. 6,685,793 and 6,630,047,
teaches methods where by such materials can be photochemcially
grafted and bonded to other substrates in the presence of amines.
However in these particular applications the concept of solution
coatings and co-crosslinking in the presence of multifunctional
acrylates is not contemplated.
[0052] Of course, as one of ordinary skill recognizes, other
fluoropolymers and fluoroelastomers not specifically listed above
may be available for use in the present invention. As such, the
above listings should not be considered limiting, but merely
indicative of the wide variety of commercially available products
that can be utilized.
[0053] The compatible organic solvent that is utilized in the
preferred embodiments of the present invention is methyl ethyl
ketone ("MEK"). However, other organic solvents including
fluorinated solvents may also be utilized, as well as mixtures of
compatible organic solvents, and still fall within the spirit and
scope of the present invention. For example, other organic solvents
contemplated include acetone, cyclohexanone, methyl isobutyl ketone
("MIBK"), methyl amyl ketone ("MAK"), tetrahydrofuran ("THF"),
methyl acetate, isopropyl alcohol ("IPA"), and mixtures thereof,
may also be utilized.
[0054] Multi-Olefinic Crosslinking Agent
[0055] The crosslinking agent of the present invention is based on
a multi-olefinic crosslinking agent. More preferably, the
multi-olefinic crosslinker in one that can be homopolymerizable.
Most preferably, the multi-olefinic crosslinker is a
fluoroalkyl-containing multi-olefinic crosslinker.
[0056] Useful fluoroalkyl containing multi-olefinic crosslinkers
including fluoroalkyl containing multi-acrylic crosslinkers, for
example, fluoroalkylene substituted acrylate or multi-acrylate mono
or multi- (meth)acryl compound bearing at least one monovalent C1
to C8 fluoroalkyl moiety (such as
CF3-,C2F5-,C3F7-,C4F9-,C5F11-,C6F13-,C7F15- or C8F17-) or
poly(hexafluoropropylene oxide) (HFPO) moiety is added to a
fluoropolymer composition optionally containing inorganic particles
("ceramer" hard coating).
[0057] The free-radically reactive fluoroalkyl or fluoroalkylene
group-containing crosslinkers are of the respective chemical
formula: R.sub.fQ(X).sub.n and (X).sub.nQR.sub.f2Q(X).sub.n), where
R.sub.f is a fluoroalkyl, R.sub.f2 is a fluoroalkylene or
perfluoropolyether, Q is a connecting group comprising an alkylene,
arylene, arylene-alkylene, or alkylene-arylene group and may
comprise a straight or branched chain connecting group which may
contain heteroatoms such as O,N, and S, X is a free-radically
reactive group selected from (meth)acryl, allyl, or vinyl groups
and n is 2 to 3. Typical Q group include: --SO.sub.2N(R)CH.sub.2CH-
.sub.2--; --SO.sub.2N(CH.sub.2CH.sub.2).sub.2--;
--(CH.sub.2).sub.m; --CH.sub.2O(CH.sub.2).sub.3--; and
--C(O)N(R)CH.sub.2CH.sub.2--, where R is H or lower alkyl of 1 to 8
carbon atoms and m is 1 to 6. Preferably the fluoroalkyl or
fluoroalkylene group is a perfluoroalkyl or perfluoroalkylene
group.
[0058] One preferred class of fluoroalkyl- or alkylene-substituted
crosslinker is the perfluorobutyl-substituted acrylate. Exemplary,
non-limiting perfluorobutyl-substituted acrylate in the present
invention includes one or more of
C.sub.4F.sub.8(CH.sub.2CH.sub.2OC(O)CH.dbd.CH.sub- .2).sub.2,
C.sub.4F.sub.9SO.sub.2N(CH.sub.2CH.sub.2OC(O)CH.dbd.CH.sub.2).s-
ub.2, or C.sub.4F.sub.8(CH.sub.2OC(O)C(CH.sub.3).dbd.CH2)2.
[0059] Other fluorochemical (meth)acrylates that may be used alone,
or as mixtures, are described in U.S. Pat. No. 6,238,798, to Kang
et al., and assigned to Minnesota Mining and Manufacturing Company
of St. Paul, Minn., and herein incorporated by reference.
[0060] HFPO Moiety and Compatibilizers
[0061] In another preferred embodiment, the coating composition
adds one or more multi-olefinic compounds bearing at least one
monovalent poly(hexafluoropropylene oxide) (HFPO) moiety and
optionally a compatibilizer such as a fluoroalkyl- or
fluoroalkylene-substituted mono or multi-acrylate such as
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub-
.2OC(O)CH.dbd.CH.sub.2,
C.sub.4F.sub.9SO.sub.2N(CH.sub.2CH.sub.2OC(O)CH
.dbd.CH.sub.2).sub.2, or
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub.-
2OC(O)C(CH.sub.3).dbd.CH.sub.2, alcohol, olefin, thiol or polythiol
to fluoropolymer curing composition. Non-limiting examples of thiol
or polythiol type of compatibilizer includes one or more of the
following:
[0062]
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub.2OC(O)CH.sub.2SH,
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub.2OC(O)CH.sub.2CH.sub.2SH,
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH.sub.2CH.sub.2SH, and
C.sub.4F.sub.9SO.sub.2N(CH.sub.3)CH(OC(O)CH.sub.2SH)CH.sub.2OC(O)CH.sub.2-
SH.
[0063] As used in the examples, unless otherwise noted, "HFPO--"
refers to the end group
F(CF(CF.sub.3)CF.sub.2O).sub.aCF(CF.sub.3)--of the methyl ester
F(CF(CF.sub.3)CF.sub.2O).sub.aCF(CF.sub.3)C(O)OCH.sub.3, wherein
"a" averages about 6.8, and the methyl ester has an average
molecular weight of 1,211 g/mol, and which can be prepared
according to the method reported in U.S. Pat. No. 3,250,808 (Moore
et al.), the disclosure of which is incorporated herein by
reference, with purification by fractional distillation.
[0064] The mono- or multi-olefinic compound bearing at least one
monovalent poly(hexafluoropropylene oxide) (HFPO) moiety preferably
is in the form of a multiacrylate. These materials are of the
formula: R.sub.fpeQ(X).sub.n wherein Rfpe is the residue of a
monovalent HFPO moiety, Q is a connecting group comprising an
alkylene, arylene, arylene-alkylene, or alkylene-arylene group and
may comprise a straight or branched chain connecting group which
may contain heteroatoms such as O,N, and S, X is a free-radically
reactive group selected from meth(acryl), allyl, or vinyl groups
and n is 2 to 3. Typical Q group include: --(CH.sub.2).sub.m--;
--CH.sub.2O(CH.sub.2).sub.3--; and --C(O)NRCH.sub.2CH.sub.2--,
where R is H or lower alkyl of 1 to 4 carbon atoms and m is 1 to
6.
[0065] One class of multi- (meth)acryl compound bearing at least
one monovalent poly(hexafluoropropylene oxide) (HFPO) moiety
comprises compounds described in U.S. Provisional Application No.
60/569,351 (Docket No. 59795US002) entitled "Fluoropolyether
Polyacryl Compounds", filed May 7, 2004, the disclosure of which is
incorporated by reference.
[0066] Other mono- and multi- (meth)acryl compounds bearing at
least one monovalent poly(hexafluoropropylene oxide) (HFPO) moiety
comprise compounds which are Michael adducts of HFPO amine
derivatives with multiacrylates described in U.S. application Ser.
No. 10/841,792, entitled "Polymerizable Compositions, Methods Of
Making The Same, And Composite Articles Therefrom," (Docket No.
59644) filed May 7, 2004, the disclosure of which is incorporated
by reference.
[0067] Surface Modified Nanoparticles
[0068] The mechanical durability of the resultant low refractive
index layers 20 can be enhanced by the introduction of surface
modified inorganic particles.
[0069] These inorganic particles can have a substantially
monodisperse size distribution or a polymodal distribution obtained
by blending two or more substantially monodisperse distributions.
The inorganic oxide particles are typically non-aggregated
(substantially discrete), as aggregation can result in
precipitation of the inorganic oxide particles or gelation of the
hardcoat. The inorganic oxide particles are typically colloidal in
size, having an average particle diameter of 5 nanometers to 100
nanometers. These size ranges facilitate dispersion of the
inorganic oxide particles into the binder resin and provide
ceramers with desirable surface properties and optical clarity. The
average particle size of the inorganic oxide particles can be
measured using transmission electron microscopy to count the number
of inorganic oxide particles of a given diameter. Inorganic oxide
particles include colloidal silica, colloidal titania, colloidal
alumina, colloidal zirconia, colloidal vanadia, colloidal chromia,
colloidal iron oxide, colloidal antimony oxide, colloidal tin
oxide, and mixtures thereof. Most preferably, the particles are
formed of silicon dioxide (SiO.sub.2).
[0070] The surface particles are modified with polymer coatings
designed to have alkyl or fluoroinated alkyl groups, and mixtures
thereof, that have reactive functionality towards the
fluoropolymer. Such functionalities include mercaptan, vinyl,
acrylate and others believed to enhance the interaction between the
inorganic particles and low index fluoropolymers, especially those
containing chloro, bromo, iodo or alkoxysilane cure site monomers.
Specific surface modifying agents contemplated by this invention
include but are not limited to 3
-methacryloxypropyltrimethoxysilane A174 OSI Specialties Chemical),
vinyl trialkoxy silanes such as trimethoxy and triethoxy silane and
hexamethydisilizane (available from Aldrich Co).
[0071] These vinylidene fluoride containing fluoropolymers are
known to enable grafting with chemical species having nucleophilic
groups such as --NH.sub.2, --SH, and --OH via dehydrofluorination
and Michael addition processes.
[0072] Photoinitiators and Additives
[0073] To facilitate curing, polymerizable compositions according
to the present invention may further comprise at least one
free-radical photoinitiator. Typically, if such an initiator
photoinitiator is present, it comprises less than about 10 percent
by weight, more typically less than about 5 percent of the
polymerizable composition, based on the total weight of the
polymerizable composition.
[0074] Free-radical curing techniques are well known in the art and
include, for example, thermal curing methods as well as radiation
curing methods such as electron beam or ultraviolet radiation.
Further details concerning free radical thermal and
photopolymerization techniques may be found in, for example, U.S.
Pat. No. 4,654,233 (Grant et al.); U.S. Pat. No. 4,855,184 (Klun et
al.); and U.S. Pat. No. 6,224,949 (Wright et al.).
[0075] Useful free-radical photoinitiators include, for example,
those known as useful in the UV cure of acrylate polymers. Such
initiators include benzophenone and its derivatives; benzoin,
alpha-methylbenzoin, alpha-phenylbenzoin, alpha-allylbenzoin,
alpha-benzylbenzoin; benzoin ethers such as benzil dimethyl ketal
(commercially available under the trade designation "IRGACURE 651"
from Ciba Specialty Chemicals Corporation of Tarrytown, N.Y.),
benzoin methyl ether, benzoin ethyl ether, benzoin n-butyl ether;
acetophenone and its derivatives such as
2-hydroxy-2-methyl-1-phenyl-1-propanone (commercially available
under the trade designation "DAROCUR 1173" from Ciba Specialty
Chemicals Corporation) and 1-hydroxycyclohexyl phenyl ketone
(commercially available under the trade designation "IRGACURE 184",
also from Ciba Specialty Chemicals Corporation);
2-methyl-1-[4-methylthio)phenyl]-2-(4-m- orpholinyl)-1-propanone
commercially available under the trade designation "IRGACURE 907",
also from Ciba Specialty Chemicals Corporation);
2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone
commercially available under the trade designation "IRGACURE 369"
from Ciba Specialty Chemicals Corporation); aromatic ketones such
as benzophenone and its derivatives and anthraquinone and its
derivatives; onium salts such as diazonium salts, iodonium salts,
sulfonium salts; titanium complexes such as, for example, that
which is commercially available under the trade designation "CGI
784 DC", also from Ciba Specialty Chemicals Corporation);
halomethylnitrobenzenes; and mono- and bis-acylphosphines such as
those available from Ciba Specialty Chemicals Corporation under the
trade designations "IRGACURE 1700", "IRGACURE 1800", "IRGACURE
1850","IRGACURE 819" "IRGACURE 2005", "IRGACURE 2010", "IRGACURE
2020" and "DAROCUR 4265". Combinations of two or more
photoinitiators may be used. Further, sensitizers such as
2-isopropyl thioxanthone, commercially available from First
Chemical Corporation, Pascagoula, Miss., may be used in conjunction
with photoinitiator(s) such as "IRGACURE 369".
[0076] More preferably, the initiators used in the present
invention are either "DAROCURE 1173" or "ESACURE.RTM. KB-1", a
benzildimethylketal photoinitiator available from Lamberti S.p.A of
Gallarate, Spain.
[0077] Alternatively, or in conjunction herewith, the use of
thermal initiators may also be incorporated into the reaction
mixture. Useful free-radical thermal initiators include, for
example, azo, peroxide, persulfate, and redox initiators, and
combinations thereof.
[0078] Those skilled in the art appreciate that the coating
compositions can contain other optional adjuvants, such as,
surfactants, antistatic agents (e.g., conductive polymers),
leveling agents, photosensitizers, ultraviolet ("UV") absorbers,
stabilizers, antioxidants, lubricants, pigments, dyes,
plasticizers, suspending agents and the like.
[0079] The reaction mechanism for forming the low refractive index
composition according to one preferred approach (REACTION MECHANISM
1) is described in further detail below:
Reaction Mechanism 1
[0080] The low refractive index coating composition of the present
invention used to form layer 20, in this preferred approach, is
formed by first dissolving a fluoropolymer in a suitable organic
solvent and then reactively photo-crosslinking the fluoropolymer
with a fluoroalkyl-containing multiolefinic (here acrylate)
crosslinker. The mechanism for forming the coating composition
involves two distinct steps as described below:
[0081] Step 1: Dissolving of Fluoropolymer and Introduction of m
Fluoroalkyl Containing Multiolefinic (here acrylate) Crosslinker to
Fluoropolymer and Subsequent Application to a Substrate
Material
[0082] In Reaction Mechanism 1, a fluoropolymer as described above
is first dissolved in a compatible organic solvent. Preferably, the
solution is about 10% by weight fluoropolymer and 90% by weight
organic solvent. Optionally, surface modified nanoparticles as
described above may be added to the fluoropolymer solution in
amounts not exceeding about 5-10% by weight of the overall low
refractive index composition.
[0083] The compatible organic solvent that is utilized in the
preferred embodiments of the present invention is methyl ethyl
ketone ("MEK"). However, other organic solvents may also be
utilized, as well as mixtures of compatible organic solvents, and
still fall within the spirit and scope of the present invention.
For example, other organic solvents contemplated include methyl
isobutyl ketone ("MIBK"), methyl amyl ketone ("MAK"),
tetrahydrofuran ("THF"), isopropyl alcohol ("IPA"), or mixtures
thereof, may also be utilized.
[0084] Next, the fluoroalkyl-containing multiolefinic (here
acrylate) crosslinker is added to the dissolved fluoropolymer. The
resultant composition is then applied as a wet layer either (1)
directly to an optical substrate or hardcoated optical substrate,
or (2) to a high refractive index layer, or (3) to a release layer
of a transferable film. The optical substrate could be glass or a
polymeric material such as polyethylene terepthalate (PET).
[0085] Next, the wet layer is dried at between about 100 and 120
degrees Celsius for about ten minutes to form a dry layer (i.e.
coated subject). Preferably, this is accomplished by introducing
the substrate having the wet layer to an oven.
[0086] Step 2: Photocrosslinking Reaction
[0087] Next, the coated subject is irradiated with an ultraviolet
light source to induce photocrosslinking of the C.dbd.C containing
silane compound and the multifunctional (meth)acrylate to the
fluoropolymer backbone. Preferably, the coated subject is subjected
to ultraviolet radiation such as by H-bulb, D-bulb or by a 254
nanometer (nm) lamp in one or more passes along a conveyor belt to
form the low refractive index layer 20. The UV processor preferably
used is Fusion V, Model MC-6RQN with H-bulb, made by Fusion UV
Systems, Inc. of Gaithersburg, Md.
[0088] Alternatively, the coated subject can be thermally
crosslinked by applying heat and a suitable radical initiator such
as a peroxide compound.
[0089] The reaction mechanism is one in which the acrylate
component of the fluoroalkyl-containing crosslinker reacts with the
fluoropolymer backbone. To enhance this reaction, the fluoropolymer
preferably has reaction site monomers (i.e. the fluoropolymer has a
plurality of bromo-, iodo-, and chloro-containing cure sites) or
other copolymers to provide further crosslinking sites.
EXAMPLES
[0090] The following paragraphs illustrate, via a specific set of
example reactions and experimental methodologies, the improvements
of each of the component steps for forming the low refractive index
composition of the present invention.
[0091] A. Ingredients:
[0092] The ingredients used for forming the various coatings of
this invention are summarized in the following paragraphs.
[0093] Dyneon.TM. THV.TM. 220 Fluoroplastic (20 MFI, ASTM D 1238)
is available as either a 30% solids latex grade under the trade
name of Dyneon.TM. THV.TM. 220D Fluoroplastic dispersion, or as a
pellet grade under the trade name of Dyneon.TM. THV.TM. 220G. Both
are available from Dyneon LLC of St. Paul, Minn. In the case of
Dyneon.TM. THV.TM. 220D, a coagulation step is necessary to isolate
the polymer as a solid resin. The process for this is described
below.
[0094] Dyneon.TM. FT 2430 and Dyneon.TM. FC 2145 fluoroelastomers
are about 70 weight percent fluorine terpolymer and about 66 weight
percent fluorine copolymers respectively, both available from
Dyneon LLC of St. Paul, Minn. and were used as received.
[0095] Trimethylolpropane triacrylate SR 351 ("TMPTA") and
Di-Pentaerythritol tri acrylate (SR 399LV) were obtained from
Sartomer Company of Exton, Pa. and used as received.
[0096] Acryloyl chloride was obtained from Sigma-Aldrich and used
without further purification.
[0097] 3-methacryloxypropyltrimethoxysilane available as A174 OSI
Specialties Chemical was used as received.
[0098] 3-aminopropyl triethoxy silane (3-APS) is available form
Aldrich Chemical of Milwaukee, Wis. and was used as received.
[0099] A1106- Silquest, manufactured by Osi Specialties (GE
Silicones) of Paris, France.
[0100] "Darocur 1173" 2-hydroxy 2-methyl 1-phenyl propanone UV
photoinitiator, and Irgacure.TM. 819 were obtained from Ciba
Specialty Products of Terrytown, N.Y. and used as received.
[0101] "KB-1" benzyl dimethyl ketal UV photoinitiator was obtained
from Sartomer Company of Exton, Pa. and was used as received.
[0102] Dowanol.TM., 1-methoxy-2-propanol was obtained from
Sigma-Aldrich of Milwaukee, Wis. and used as received.
[0103] SR295, mixture of pentaerythritol tri and tetraacrylate, CN
120Z, Acrylated bisphenol A, SR339, Phenoxyethyl acrylate, were
obtained from Sartomer Chemical Company of Exton, Pa. and used as
received.
[0104] (3-Acryloxypropyl)trimethoxysilane, was obtain from Gelest
of Morrisville, Pa. and was used as received.
[0105] A1230, polyether silane was obtained from OSI Specialties
and was used as received.
[0106] Buhler zirconia (ZrO.sub.2), grades Z-WO and Z-WOS, were
obtained from Buhler, Uzweil Switzerland and modified as described
in the preparation of (S3) and (S4) described below.
[0107] FBSEE (C.sub.4F.sub.9SO.sub.2N(C.sub.2H.sub.4OH).sub.2), a
fluorochemical diol, can be prepared as described in column 5, line
31 and in FIG. 9 of U.S. Pat. No. 3,734,962 (1973).
[0108] FBSAA
(C.sub.4F.sub.9SO.sub.2N(CH.sub.2CH.sub.2OC(O)CH.dbd.CH.sub.2-
).sub.2) is prepared by the procedure in column 25 lines 49-63 of
U.S. Pat. No. 6,238,798.
[0109] Oligomeric hexafluoropropylene oxide methyl ester
(HFPO--C(O)OCH.sub.3,) can be prepared according to the method
reported in U.S. Pat. No. 3,250,808 (Moore et al.). The broad
product distribution of oligomers obtained from this preparation
can be fractionated according to the method described in U.S.
patent application Ser. No. 10/331816, filed Dec. 30, 2002. This
step yields the higher molecular weight distribution of oligomers
used in this description wherein the number average degree of
polymerization is about 6.3, and with an average molecular weight
of 1,211 g/mol.
[0110] 1. Preparation of Hexafluoropropylene Oxide
N-methyl-1,3-propanedia- mine Adduct
[0111] A 1-liter round-bottom flask was charged with 291.24 g
(0.2405 mol) of FC-1 and 21.2 g (0.2405 mol)
N-methyl-1,3-propanediamine, both at room temperature, resulting in
a cloudy solution. The flask was swirled and the temperature of the
mixture rose to 45.degree. C., and to give a water--white liquid,
which was heated overnight at 55.degree. C. The product was then
placed on a rotary evaporator at 75.degree. C. and 28 inches of Hg
vacuum to remove methanol, yielding 301.88 g of a viscous slightly
yellow liquid, the hexafluoropropylene oxide
N-methyl-1,3-propanediamine adduct.
[0112] 2. Preparation of HFPO-acrylate- (HFPO-1)
[0113] To a 250 ml roundbottom flask was charged with 4.48 g (15.2
mmoles, based on a nominal MW of 294) of trimethylolpropane
triacrylate (TMPTA, Sartomer SR351), 4.45 g of tetrahydrofuran
(THF), and 1.6 mg of phenothiazine and placed in an oil bath at
55C. Next, in a 100 ml jar was dissolved 20 g (15.78 mmole, MW
1267.15) hexafluoropropylene oxide N-methyl-1,3-propanediamine
adduct in 32 g THF. This solution was placed in a 60 ml dropping
funnel with pressure equalizing sidearm, the jar rinsed with about
3 ml of THF, which was also added to the dropping funnel. The
contents of the funnel were added over 38 minutes under an air
atmosphere to the TMPTA/THF/phenothiazine mixture. The reaction was
cloudy at first, but cleared at about 30 minutes. Twenty minutes
after the addition was complete, the reaction flask was placed on a
rotary evaporator at 45-55 rpm under 28 inches of vacuum to yield
24.38 g of a clear, viscous yellow liquid, that was characterized
by NMR and HPLC/mass spectroscopy.
[0114] 3. Preparation of
HFPO-C(O)N(H)C(CH.sub.2OH).sub.2CH.sub.2CH.sub.3 Starting
Material
[0115] To a 500 ml 3 necked flask equipped with a stir bar and
reflux condenser was charged 11.91 g (0.1 mol)
H.sub.2NC(CH.sub.2OH).sub.2CH.sub- .2CH.sub.3 and 60 g THF. Next
via dropping funnel was added 121.1 g (0.1 mol) HFPO-C(O)OCH.sub.3
over about 80 min at a bath temperature of about 85 degrees
Celsius. The reaction was cloudy at first, but became clear about 1
h into the reaction. After addition was complete, the heating bath
was shut off and the reaction was allowed to cool for 3 days. The
material was concentrated at 55 degrees Celsius under aspirator
vacuum to yield 130.03 g of a light-colored syrup. NMR analysis
showed the product to be an 87:13 mixture of the structures (5) and
(6) as follows: 2
[0116] 4. Preparation of HFPO-acrylate- (HFPO-3)
[0117] To a 250 ml 3 necked round bottom flask equipped with
overhead stirrer was charged 65 g (0.05 mol) of
HFPO-C(O)N(H)C(CH.sub.2OH).sub.2CH- .sub.2CH.sub.3, the product
mixture generated above, 12.65 g (0.125 mol) triethylamine and 65 g
ethyl acetate. To the flask at room temperature was added 11.31
g(0.125 mol) acryloyl chloride using a pressure-equalizing dropping
funnel over 12 min, with the reaction temperature rising from 25 to
a maximum of 40.degree. C. The dropping funnel was rinsed with 5 g
additional ethyl acetate that was added to the reaction flask, that
was then placed in a 40.degree. C. bath and allowed to react for 2
hours and 10 min additional time. The organic layer was then
successively washed with 65 g 2% aqueous sulfuric acid, 65 g 2%
aqueous sodium bicarbonate, and 65 g water, dried over anhydrous
magnesium sulfate, filtered, treated with 16 mg methoxyhydroquinone
(MEHQ), and concentrated on a rotary evaporator at 45.degree. C. to
yield 62.8 g of crude product. The next 35 g of this material was
chromatographed on 600 ml of silica gel (SX0143U-3, Grade 62,
60-200 mesh, EM Science) using 25:75 ethyl acetate: heptane as an
eluent. The first two fractions were 250 ml in volume, the
remaining fractions were 125 ml in volume. Fractions 4-10 were
combined, 8 mg MEHQ was added to the fractions, and solvent was
removed on a rotary evaporator at 55C to provide 25.36 g of product
that was analyzed by NMR, and found to be an 88:12 mixture of the
structures (7) and (8). 3
[0118] 5. Preparation of modified 20-nm colloidal silicon dioxide
particles
[0119] 15 g of 2327 (20-nm ammonium stabilized colloidal silica
sol, 41% solids; Nalco, Naperville, Ill.) were placed in a 200 ml
glass jar. A solution of 10 g of 1-methoxy-2-propanol (Aldrich)
containing 0.57 g of vinyltrimethoxysilane (Gelest, Inc. of
Tullytown, Pa.) was prepared in a separate flask. The
vinyltrimethoxysilane solution was added to the glass jar while the
silica sol was stirred. The flask was then rinsed with an
additional 5-ml of solvent and added to the stirred solution. After
complete addition, the jar was capped and placed in an oven at 90
degrees Celsius for about 20 hours. The sol was then dried by
exposure to gentle airflow at room temperature. The powdery white
solid was collected and dispersed in 50 ml of TfF solvent. 2.05 g
of HMDS (excess) were slowly added to the THF silica sol, and,
after addition, the jar was capped and placed in an ultrasonic bath
for about 10 hours. Subsequently, the organic solvent was removed
by a rotovap and the remaining white solid heated at 100 degrees
Celsius overnight for further reaction and removal of volatile
species. The resultant particles are noted below as vinyl
modified/HMDS particles.
[0120] 15 g of 2327 (20 nm ammonium stabilized colloidal silica
sol, 41% solids; Nalco, Naperville, Ill.) were placed in a 200-ml
glass jar. A solution of 10 g of 1-methoxy-2-propanol (Aldrich)
containing 0.47 g of 3-(Trimethoxysilyl)propylmethacrylate (Gelest,
Inc., Tullytown, Pa.) was prepared in a separate flask. The
3-(Trimethoxysilyl)propylmethacrylate solution was added to the
glass jar while the silica sol was stirred. The flask was then
rinsed with an additional 5 ml of solvent and added to the stirred
solution. After complete addition, the jar was capped and placed in
an oven at 90 degrees Celsius for about 20 hours. The sol was then
dried by exposure to gentle airflow at room temperature. The
powdery white solid was collected and dispersed in 50 ml of THF
solvent. 2.05 g of HMDS (excess) were slowly added to the THF
silica sol, and, after addition, the jar was capped and placed in
an ultrasonic bath for about 10 hours. Subsequently, the organic
solvent was removed by a rotovap and the remaining white solid
heated at 100 degrees Celsius overnight for further reaction and
removal of volatile species. The resultant particles are noted
below as A-174/HMDS particles.
[0121] 6. Preparation of Modified Fumed Silica
[0122] The synthesis of partially acrylic-modified fumed SiO.sub.2
was prepared by first making a sol of 2 g of SiO.sub.2 (380
m.sup.2/g) and 100 ml of 1-methoxy-2-propanol (Aldrich) in a glass
jar. 4 g of ammonium hydroxide (30% aqueous solution) and 20 g
distilled water were then added slowly into the solution upon
stirring. The mixture became a gel. A solution of 20 g of
1-methoxy-2-propanol (Aldrich) containing 0.2 g of
3-(Trimethoxysilyl)propylmethacrylate (Aldrich) was prepared in a
separate flask.
[0123] The (trimethoxysilyl)propylmethacrylate solution was added
to the glass jar while stirring. The flask was then rinsed with an
additional 5-10 ml of the solvent and subsequently added to the
stirred solution. After complete addition, the jar was capped and
placed in an ultrasonic bath at 80 degrees Celsius for between 6
and 8 hours. The solution was then dried in a flow-through oven at
room temperature. The powdery white solid was collected and
dispersed into 50 ml of THF solvent. 2.05 g of HMDS (excess) was
slowly added to the THF powder solution, and, after addition, the
jar was capped and placed in an ultrasonic bath for about 10 hours.
Subsequently, the organic solvent was removed by a rotovap and the
white solid was heated at 100 degrees Celsius overnight for further
reaction and removal of volatile species. The resultant particles
are noted below as A-174/F-SiO.sub.2 particles.
[0124] 7. Preparation of Particles modified by vinyltriethoxysilane
and HMDS
[0125] By ultrasonication, a sol containing 2 g of fumed SiO.sub.2
(380 m.sup.2/g) and 100 ml of 1-methoxy-2-propanol (Aldrich) was
prepared in a glass jar. 4 g of ammonium hydroxide (30% aqueous
solution) and 20 g distilled water were then added slowly into the
solution with stirring. The mixture became a gel. A solution of 20
g of 1-methoxy-2-propanol (Aldrich) containing 0.2 g of vinyl
triethoxysilane (Gelest, Inc., Tullytown, Pa.) was prepared in a
separate flask. The solution was added to the glass jar while
stirring. The flask was then rinsed with an additional 5-10 ml of
the solvent and added to the stirred solution. After complete
addition, the jar was capped and placed in an ultrasonic bath at 80
degrees Celsius for between 6 to 8 hours. The solution was then
dried in gentle airflow at room temperature. The powdery white
solid was collected and dispersed into 50 ml of THF solvent. To the
dispersed THF sol was slowly added 2.05 g of HMDS (excess). After
addition, the jar was capped and placed in an ultrasonic bath for
about 10 hours. Subsequently, the organic solvent was removed by a
rotovap and the remaining white solid was heated at 100 degrees
Celsius overnight for further reaction and removal of volatile
species. The resultant particles are noted below as V/F--SiO.sub.2
particles.
[0126] B. Experimentation and Verification
[0127] The following paragraphs illustrate, via a specific set of
example reactions and experimental methodologies, the improvements
of each of the component steps for forming the low refractive index
composition of the present invention.
EXAMPLE 1
Photocrosslinking Fluoropolymers with Fluoroalkyl Substituted
Multiacrylate Exemplified by FBSAA
[0128] Brominated fluoroelastomer E-15742, or iodinated
fluoroelastomer E18402 were each dissolved individually in
containers with either MEK or ethyl acetate at 10 weight percent by
shaking at room temperature. The prepared fluoropolymer solutions
were then combined with FBSAA in various ratios. The mixed
fluoropolymer/FBSAA solutions were subsequently coated at a dry
thickness of about 1-2 mil using a 40 mil thickness blocked coater
onto PET or hardcoated PET. The coated films were dried briefly and
subjected to heating at 100-140 degrees Celsius for 2 minutes.
[0129] Subsequently the films were subjected to UV (H-bulb)
irradiation by 3 passes at the speed of 35 feet per minute.
Alternatively, the films were subjected to UV irradiation from a
254-nm bulb using a similar approach. After UV irradiation, the
cured films were removed from substrates and subsequently immersed
into MEK solvent for dissolving the cured films. After overnight,
the cured films remained insoluble as indicated in Table 1.
EXAMPLE 2
Photocrosslinking Fluoropolymers with Hydrocarbon Multiacrylate
TMPTA
[0130] Brominated fluoroelastomer E-15742, or iodinated
fluoroelastomer E-18402 were each dissolved individually in
containers with either MEK or ethyl acetate at 10 weight percent by
shaking at room temperature. The prepared fluoropolymer solutions
were then combined with TMPTA in various ratios. The mixed
fluoropolymer/TMPTA solutions were subsequently coated at a dry
thickness of about 1-2-mil using a 0-mil thickness blocked coater
onto PET or hardcoated PET. The coated films were dried briefly,
then subjected to heating at 100-140C for 2 minutes.
[0131] Subsequently the films were subjected to UV (H-bulb)
irradiation by 3 passes at the speed of 35 feet per minute.
Alternatively, the films were subjected to UV irradiation from a
254 nm bulb using a similar approach. After UV irradiation, the
cured films were removed from substrates and subsequently immersed
into MEK solvent for dissolving the cured films. After overnight,
the cured films remained insoluble as indicated in Table 1.
EXAMPLE 3
Photocrosslinking Fluoropolymers with Perfluoropolyether
Substituted Multiacrylates (HFPO-acrylate-1 or HFPO-acrylate-3)
[0132] Brominated fluoroelastomer E-15742, or lodinated
fluoroelastomer E-18402 were each dissolved individually in
containers with either MEK or ethyl acetate at 10 weight percent by
shaking at room temperature. The prepared fluoropolymer solutions
were then combined with HFPO-acrylate-1 or HFPO-acrylate-3 in
various ratios. The mixed fluoropolymer/HFPO-acryla- te-1 or
fluoropolymer/HFPO-acrylate-3 solutions were subsequently coated at
a dry thickness of about 1-2-mil using a 40-mil thickness blocked
coater onto PET or a hardcoated PET. The coated films were dried
briefly, then subjected to heating at 100-140 degrees Celsius for 2
minutes.
[0133] Subsequently the films were subjected to UV (H-bulb)
irradiation by 3 passes at the speed of 35 feet per minute.
Alternatively, the films were subjected to UV irradiation from a
254 nm bulb using a similar approach. After UV irradiation, the
cured films were removed from substrates and subsequently immersed
into MEK solvent for dissolving the cured films. After overnight,
the cured films remained insoluble as indicated in Table 1.
EXAMPLE 4
Photocrosslinking Fluoropolymers with Perfluoropolyether
Substituted Multiacrylates (HFPO-acrylate-1) and A174 Modified
Particles
[0134] Brominated fluoroelastomer E-15742, or iodinated
fluoroelastomer E-18402 were each dissolved individually in
containers with either MEK or ethyl acetate at 10 weight percent by
shaking at room temperature. The prepared fluoropolymer solutions
were then combined with HFPO-acrylate-1 and A174 modified 20-nm
sized SiO.sub.2 in a ratio described in Table 1. The resultant
solutions were subsequently coated at a dry thickness of about 1-2
mil using a 40 mil thickness blocked coater onto PET or a
hardcoated PET. The coated films were dried briefly, then subjected
to heating at 100-140 degrees Celsius for 2 minutes.
[0135] Subsequently the films were subjected to UV (H-bulb)
irradiation by 3 passes at the speed of 35 feet per minute.
Alternatively, the films were subjected to UV irradiation from a
254-nm bulb using a similar approach. After UV irradiation, the
cured films were removed from substrates and subsequently immersed
into MEK solvent for dissolving the cured films. After overnight,
the cured films remained insoluble as indicated in Table 1.
1TABLE 1 Crosslinking fluoropolymers with FBSAA, TMPTA and
perfluoropolyether multiacrylates # of Passes A174:HMDS under (1:1)
Time UV % % % % HFPO- % HFPO- Modified % Temp. Heated (H
Crosslinking E15742 E18402 FBSAA acrylate-1 % TMPTA acrylate-3
particle KB-1 Heated (min) bulb) Test 97 3 0 0 0 0 1 120 5 3
crosslinked 95 5 0 0 0 0 1 120 5 3 crosslinked 93 7 0 0 0 0 1 120 5
3 crosslinked 97 3 0 0 0 0 1 120 5 3 crosslinked 95 5 0 0 0 0 1 120
5 3 crosslinked 93 7 0 0 0 0 1 120 5 3 crosslinked 97 0 0 3 0 0 0 1
120 5 3 crosslinked 95 0 0 5 0 0 0 1 120 5 3 crosslinked 93 0 0 7 0
0 0 1 120 5 3 crosslinked 90 0 0 10 0 0 0 1 120 5 3 crosslinked 0
97 0 3 0 0 0 1 120 5 3 crosslinked 0 95 0 5 0 0 0 1 120 5 3
crosslinked 0 93 0 7 0 0 0 1 120 5 3 crosslinked 0 90 0 10 0 0 0 1
120 5 3 crosslinked 95 0 0 0 5 0 0 1 120 5 3 crosslinked 90 0 0 0
10 0 0 1 120 5 3 crosslinked 0 95 0 0 5 0 0 1 120 5 3 crosslinked 0
90 0 0 10 0 0 1 120 5 3 crosslinked 95 0 0 0 0 5 0 1 120 5 3
crosslinked 90 0 0 0 0 10 0 1 120 5 3 crosslinked 0 95 0 0 0 5 0 1
120 5 3 crosslinked 0 90 0 0 0 10 0 1 120 5 3 crosslinked 65 0 0 0
0 5 30 1 120 5 3 crosslinked 0 65 0 0 0 5 30 1 120 5 3
crosslinked
EXAMPLE 5
Scratch Resistance Test on Control Fluoropolymers After UV
Treatment
[0136] Brominated fluoroelastomer E-15742, or iodinated
fluoroelastomer E-18402 were each dissolved individually in
containers with either MEK or ethyl acetate at 3 weight percent by
shaking at room temperature. The prepared fluoropolymer solutions
were subsequently coated at a dry thickness of about 100 nm using a
number 3 metering rod obtained from GARDCO onto hardcoated PET. The
coated films were dried briefly, then subjected to heating at
100-140C for 2 minutes.
[0137] Subsequently, the films were subjected to UV (H-bulb)
irradiation by 3 passes at the speed of 35 feet per minute. After
UV irradiation, the scratch resistance of the cured films were
evaluated as indicated in Table 2.
EXAMPLE 6
Scratch Resistance Test on Fluoropolymers Photocrosslinked by
Fluoroalkyl Substituted Multiacrylate Exemplified by FBSAA
[0138] Brominated fluoroelastomer E-15742, or iodinated
fluoroelastomer E18402 were each dissolved individually in
containers with either MEK or ethyl acetate at 10 weight percent by
shaking at room temperature. The prepared fluoropolymer solutions
were then combined with FBSAA in various ratios. The mixed
fluoropolymer/FBSAA solutions were subsequently coated at a dry
thickness of about 100 nm using a number 3 metering rod obtained
from GARDCO onto hardcoated PET. The coated films were dried
briefly, then subjected to heating at 100-140 degrees Celsius for 2
minutes.
[0139] Subsequently the films were subjected to UV (H-bulb)
irradiation by 3 passes at the speed of 35 feet per minute. After
UV irradiation, the scratch resistance of the cured films were
evaluated as indicated in Table 2.
EXAMPLE 7
Scratch Resistance Test on Fluoropolymers Photocrosslinked by
Hydrocarbon Multiacrylate TMPTA
[0140] Brominated fluoroelastomer E-15742, or iodinated
fluoroelastomer E18402 were each dissolved individually in
containers with either MEK or ethyl acetate at 10 weight percent by
shaking at room temperature. The prepared fluoropolymer solutions
were then combined with TMPTA in various ratios. The mixed
fluoropolymer/TMPTA solutions were subsequently coated at a dry
thickness of about 100 nm using a number 3 metering rod obtained
from GARDCO onto hardcoated PET. The coated films were dried
briefly, then subjected to heating at 100-140C for 2 minutes.
[0141] Subsequently the films were subjected to UV (H-bulb)
irradiation by 3 passes at the speed of 35 feet per minute. After
UV irradiation, the scratching resistance of the cured films were
evaluated as indicated in Table 2.
EXAMPLE 8
Scratch Resistance Test on Fluoropolymers Photocrosslinked by
Perfluoropolyether Substituted Multiacrylates (HFPO-acrylate-1 or
HFPO-acrylate-3)
[0142] Brominated fluoroelastomer E-15742, or iodinated
fluoroelastomer E-18402 were each dissolved individually in
containers with either MEK or ethyl acetate at 10 weight percent by
shaking at room temperature. The prepared fluoropolymer solutions
were then combined with HFPO-acrylate-1 or HFPO-acrylate-3 in
various ratios. The mixed fluoropolymer/HFPO-acryla- te-1 (or
fluoropolymer/HFPO-acrylate-3) solutions were subsequently coated
at a dry thickness of about 100 nm using a number 3 metering rod
obtained from GARDCO onto hardcoated PET. The coated films were
dried briefly, then subjected to heating at 100-140 degrees Celsius
for 2 minutes.
[0143] Subsequently the films were subjected to UV (H-bulb)
irradiation by 3 passes at the speed of 35 feet per minute. After
UV irradiation, the scratch resistance of cured films were
evaluated as indicated in Table II.
EXAMPLE 9
Scratch Resistance Test on Fluoropolymers Photocrosslinked by
Perfluoropolyether Substituted Multiacrylates (HFPO-acrylate-1) and
A174 Modified Particles
[0144] Brominated fluoroelastomer E-15742, or iodinated
fluoroelastomer E-18402 were each dissolved individually in
containers with either MEK or ethyl acetate at 10 weight percent by
shaking at room temperature. The prepared fluoropolymer solutions
were then combined with HFPO-acrylate-1 and A174 modified 20 nm
sized SiO.sub.2 in a ratio described in Table I. The mixed
fluoropolymer/HFPO-acrylate-1 and A174 modified 20 nm
sized.sub.SiO2 solutions were subsequently coated at a dry
thickness of about 100 nm using a number 3 metering rod obtained
from GARDCO onto hardcoated PET. The coated films were dried
briefly, then subjected to heating at 100-140 degrees Celsius for 2
minutes.
[0145] Subsequently the films were subjected to UV (H-bulb)
irradiation by 3 passes at the speed of 35 feet per minute. After
UV irradiation, the scratching resistance of the cured films were
evaluated as indicated in Table 2.
2TABLE 2 Improved scratching resistance by crosslinking with
fluoroalkyl multiacrylate and optional surface modified particles %
A174:H 132347-90 MDS (multi (1:1) Coat Time # of Passes % %
functional Modified % Bar Temp. Heated under UV Scratch Test
Substrate Wt % E15742 E18402 acrylate) particle KB-1 used Heated
(min) (H bulb) (10 Times) Hard Coat 0 100 0 0 0 1 100 nm 120 5 3
Heavily scratched Hard Coat 0 0 100 0 0 1 100 nm 120 5 3 Heavily
scratched Hard Coat 3 97 0 3 0 1 100 nm 120 5 3 Light scratch Hard
Coat 3 95 0 5 0 1 100 nm 120 5 3 Light scratch Hard Coat 3 93 0 7 0
1 100 nm 120 5 3 Light scratch Hard Coat 3 90 0 10 0 1 100 nm 120 5
3 Light scratch Hard Coat 3 0 97 3 0 1 100 nm 120 5 3 Light scratch
Hard Coat 3 0 95 5 0 1 100 nm 120 5 3 Light scratch Hard Coat 3 0
93 7 0 1 100 nm 120 5 3 Light scratch Hard Coat 3 0 90 10 0 1 100
nm 120 5 3 Light scratch Hard Coat 3 65 0 5 30 1 100 nm 120 5 3
Light scratch Hard Coat 3 0 65 5 30 1 100 nm 120 5 3 Light
scratch
[0146] As Tables 1 and 2 confirm, the low refractive index
compositions introducing a fluoroalkyl-containing multi-olefinic
crosslinker to a fluoropolymer showed improved mechanical
properties in terms of scratch resistance as compared with coatings
not introducing a fluoro-component to the crosslinker (i.e.
consisting strictly of a hydrocarbon-based multi-olefinic
crosslinker--or the standard). Further, the mechanical strength and
scratch resistance the low refractive index composition can be
enhanced by the addition of surface functionalized nanoparticles
into the fluoropolymer compositions. Providing functionality to the
nanoparticles enhances the interactions between the fluoropolymers
and such functionalized particles. Further, the introduction of
HFPO moieties with and without compatibilizers also showed
improvement over the standard composition. Fluoropolymers as seen
in Table 1 can be crosslinked by fluorinated multifunctional
olefinic crosslinkers confirmed by solvent swelling tests.
[0147] While the invention has been described in terms of preferred
embodiments, it will be understood, of course, that the invention
is not limited thereto since modifications may be made by those
skilled in the art, particularly in light of the foregoing
teachings.
* * * * *